Drum brake device

ABSTRACT

A drum device is provided that functions as a very stable leading-trailing (LT) type when the service brake is applied, and as a highly effective duo-servo (DS) type with very little fluctuation in stroke when the parking brake is applied, in which strange noises are not generated, and any impact load is not applied to any of the components, thus enabling a lighter device. A shoe clearance adjustment device ( 12 ), adjacent to a service brake actuator ( 8 ) is suspended between the two brake shoes ( 2, 3 ). A parking brake actuator ( 18 ) is adjacent to an anchor ( 9 ). The middle segment of a long link ( 11 ) is pivotable in the middle of the one brake shoe ( 2 ). The ends of the link are functionally engaged with the shoe clearance adjustment device ( 12 ) and the parking brake actuator ( 18 ), respectively. The parking brake actuator ( 18 ) is equipped with a stroke adjustment device.

This application is a divisional application filed under 37 CFR §1.53(b) of parent application Ser. No. 08/947,327, filed Oct. 8, 1997,now U.S. Pat. No. 6,082,505.

BACKGROUND OF THE INVENTION

This invention relates to a drum brake device. More specifically, itrelates to a drum brake device that functions as a leading-trailing (LT)type when the service brake is applied, and as a duo-servo (DS) typewhen the parking brake is applied.

This type of drum brake device has been disclosed in Australian PatentNo. AU-B1-53 491179 and U.S. Pat. No. 5,275,260. The basic brakefunctions are the same in both devices, and the structure will beexplained with reference to FIG. 17. A pair of brake shoes b, c areprovided on top of a back plate a. An anchor block d is provided betweenthe adjacent ends of one side of each brake shoe, and a hydrauliccylinder g is provided between the other adjacent ends of each brakeshoe. A parking lever j is pivoted on one end i of one brake shoe b. Anidler lever k is pivoted so as to swing on the other brake shoe c. Thefirst and second rods l, m are provided between the two brake shoes b,c, wherein one end n of the first rod l engages the parking lever j, andthe other end o engages with the idler lever k; and one end p of thesecond rod m engages one brake shoe b, while the other end q engageswith the other brake shoe c and the idler lever k.

The brake action is explained as follows. When the driver steps on thebrake pedal, the hydraulic cylinder g is pressurized, wherein the twobrake shoes b, c spread open, with the point of abutment with the anchorblock d as the fulcrum, to cause a frictional connection with therotating brake drum, not shown in the diagram, in a leading-trailingbraking action.

When the parking brake is applied, the parking lever j is pulled in thedirection of the arrow X. The force of that action is transferred insequence to the first rod l, idler lever k, and second rod m, whereinthe one brake shoe b opens with its point of abutment with the anchorblock d as the fulcrum, and to cause a frictional connection with thebrake drum. Next, the idler lever k spreads open, with the point ofabutment with the second rod as the fulcrum, causing the pivot componentof the idler lever k to press the other brake shoe c in the direction ofthe arrow Y to cause a frictional connection with the brake drum. At thesame time, the reaction force of the parking lever j is being applied inthe direction of the arrow Z on the one end i of the one brake shoe b.

If at this time, the torque is applied on the brake drum in thedirection of arrow R (uphill or downhill), the friction force of the onebrake shoe b is transferred to the second rod m, wherein its other end qpresses against the other brake shoe c, supported by the anchor block d,in a duo-servo braking action. If the torque is applied on the brakedrum in the opposite direction of arrow R, the friction force of theother brake shoe c is transferred to the second rod m, whereby its oneend p is pressed against the one brake shoe b, supported by the anchorblock d, in the same duo-servo braking action as above.

As is evident from this parking brake operation, if the other end q ofthe second rod m abuts the idler lever k and a gap exists between theother end q and the other brake shoe c, then whether the shoe c rotatesin the opposite direction of R, the piston of the hydraulic cylinder gis repelled to an amount equivalent to the gap. That is, the brake pedalis repelled which is not only disconcerting to the driver, but the pedalstroke increases in the next brake pedal application. Conversely, if theother end q of the second rod m abuts against the other brake shoe c anda gap exists between the other end q and the idler lever k, then thestroke of the parking lever j increases by an amount equivalent to thisgap; that is, the stroke of the hand lever increases. From theseperspectives, it is preferable that the gap between the other end q ofthe second rod m and either the other brake shoe c or the idler lever kbe as small as possible.

Next, FIG. 18 illustrates the concept of the automatic shoe clearancedevice which is installed in the drum brake device of U.S. Pat. No.5,275,260. The bent end y of the adjustment lever r is pivotable on theweb of brake shoe c, and one upper arm s is connected to the groove ofthe upper strut t for their interaction. Another arm is connected to thestar wheel u of the upper strut t. A spring w, stretched between theadjustment lever r and the pivot lever v, energizes the adjustment leverr in the counterclockwise direction, with the end y as the fulcrum.

Should the brake lining be worn causing the two brake shoes b, c to openby more than a prescribed value when the service brake is applied, theupper arm causes the star wheel u to rotate to automatically extend theentire length of the upper strut t, thereby maintaining a constantclearance between the brake shoes b, c and the brake drum z.

The drum brake device as described above has need of improvement in thefollowing areas:

The cumulative effect of the tolerances of each component of the parkingbrake system will inevitably create a gap between the idler lever k andthe first rod l or the second rod m, and the brake stroke becomesineffective by an amount equivalent to this gap.

Moreover, as the lining of the other brake shoe c gradually wears, thereis a gradual shift in the point at which the second rod m contacts withthe brake shoe c or the idler lever k. That is, as shown in FIG. 17, theamount of displacement δ of the brake shoe c at the brake center, andthe amount of displacement δc and δk of the brake shoe c and idler leverk respectively at the point of contact with the second rod m are definedas follows: $\begin{matrix}{{{Brake}\quad {shoe}\quad {displacement}\quad \delta \quad c} = {\frac{{H1} + {H2}}{H1} \times \delta}} & {{Formula}\quad (1)}\end{matrix}$

$\begin{matrix}{{{{Idler}\quad {lever}\quad k\quad {displacement}\quad \delta \quad k} = {\frac{{H2} + {H3}}{H3} \times \delta}},} & {{Formula}\quad (2)}\end{matrix}$

where

H1: Distance from anchor d to the brake center (pivot point of brakeshoe c and idler lever k);

H2: Distance from the brake center to the second rod m;

H3: Distance from the brake center to the first rod l;

δ: Amount of lining wear.

In this case, H3 is considerably smaller than H1, hence the displacementδk of the idler lever k will be considerably larger than thedisplacement δc of the brake shoe c. As a result, the stroke of theparking lever j will increase as the lining wears. The driver not onlyfeels a greater slackness in the hand brake, but there are concerns aswell that the lever j could interfere with other components to lessenthe effectiveness of the braking action. In addition, the stroke of theparking lever could also limit the brake size, brake offset, and otherbrake factors to constrain the degree of freedom in the brake design.

If H3 (distance from the center of rotation of the idler lever k to thefirst rod l) and H2 (distance from the same point to the second rod m)are set to be equal, and the brake drum rotates in the direction of thearrow R when the parking brake is applied, then the one brake shoe b,the parking lever j and other components will turn in tandem in the samedirection (the degree of rotation will be equivalent to the distancetraveled by the other end q of the second rod until it starts to pressagainst the other brake shoe c). FIG. 19 is a conceptual drawing of thisoperation. The double-dash broken line shows the state of the device ifthe parking brake is activated after the vehicle is stopped by theservice brake on a slope. The one ends i of both brake shoes b, c aresupported by the anchor block d. Then if the service brake is releasedin this state, the force of gravity acting on the vehicle causes thebrake drum, not shown in the diagram, to rotate in the direction of thearrow R, whereby the one brake shoe b and the parking lever j areshifted to the positions indicated by the solid line and broken linerespectively. As a result, if point s is the outlet of the parking brakepulling mechanism, then the distance from point s to the pulled part ofthe parking lever j is shortened by an amount equal to (l₁−l₂). In otherwords, the pulled part of the parking lever j is shifted in thedirection of the pull to loosen the locked parking brake pullingmechanism, thus reducing the effectiveness of the parking brake.

When the parking brake is applied, the adjacent ends of each side of theboth brake shoes move apart to spread apart the whole brake assembly. Inother words, the one end of both of the shoes also separate at once fromthe anchor block. When the brake drum which is interlocked with thewheels starts to rotate with the device in this state, both brake shoes,the rods, and other components all turn in tandem, wherein one or theother brake shoe collides against the anchor block. The noise sogenerated is not only disconcerting to the driver. Additionally, sincethis impact load is applied repeatedly on the anchor block, the strengthof the components becomes critical.

In the conventional device as disclosed in Australian Patent No.AU-B1-53 491179, the cumulative effect of the tolerances of eachcomponent will be such that the idler lever could abut against thesecond rod or play could be generated. At the very least, play will begenerated when the driver steps on the brake pedal. Accordingly, theidler lever could vibrate creating a strange noise when the vehicle isin motion or the service brake is applied. Again this noise can bedisconcerting to the driver.

In the conventional device as disclosed in U.S. Pat. No. 5,275,260 asthe lining wears, the adjustment lever becomes interlocked with thebrake shoe and moves with its point of abutment with the support blockas the fulcrum, while the pivot lever moves with its point of abutmentwith the lower strut as the fulcrum. This changes the energizing forceof the adjustment spring energizing the adjustment lever, which has anegative effect on the automatic adjustment process when only a veryminimal adjustment is required.

OBJECTS AND SUMMARY OF THE INVENTION

This invention was devised to resolve the aforementioned problems byproviding a drum brake device that functions as a very stableleading-trailing (LT) type when the service brake is applied, and as ahighly effective duo-servo (DS) type when the parking brake is applied.

To that end, it is a first object of the invention to provide to providea drum brake device in which the automatic shoe clearance adjustmentfunctions very precisely for a prolonged period of time.

The second object is to provide a drum brake device in which strangenoises are not generated.

The third object is to provide a drum brake device in which no impactload is applied to any of the components, thus enabling a lighterdevice.

The fourth object is to provide a drum brake device in which avoids thewheel being locked because of the brake shoe biting the brake drum orunusual dragging occurring between the brake lining and the brake drum.

These and other objects are obtained in a drum brake device comprisingcertain particular structure.

Claim 1 is a drum brake device comprising: a back plate, two brake shoesprovided to face each other on top of said back plate, a service brakeactuator on said back plate between one pair of first adjacent ends ofsaid brake shoes, an anchor block on said back plate between the otherpair of second adjacent ends of the brake shoes, a shoe clearanceadjustment device adjacent to said service brake actuator providedbetween said brake shoes, a parking brake actuator adjacent to saidanchor, a long link having a middle segment pivotably mounted at a pivotpoint on the middle of one brake shoe, and one end of said link and theother end of said link respectively functionally engaged to said shoeclearance adjustment device and said parking brake actuator; wherein astroke adjustment device fitted to said parking brake actuator to adjustthe stroke of said parking brake actuator in the direction of the strokeof said parking brake actuator.

Claim 2 is a drum brake device as claimed in claim 1, wherein said longlink operates in tandem with said one brake shoe when the service brakeis applied.

Claim 3 is a drum brake device as claimed in claim 1, in which said shoeclearance adjustment device senses an amount by which said pair of brakeshoes has opened and automatically adjusts the clearance between thebrake shoes and the brake drum.

Claim 4 is a drum brake device as claimed in claim 1, in which saidstroke adjustment device senses the amount by which said pair of brakeshoes has opened and automatically adjusts the stroke of said parkingbrake actuator.

Claim 5 is a drum brake device as claimed in claim 1, wherein with thepivot point in the central region of said long link as the fulcrum, theresistance to spread open said pair of the brake shoes on said otherside is greater than the resistance to spread open said pair of thebrake shoes on said one side.

Claim 6 is a drum brake device as claimed in claim 5, wherein the momentapplied to the second adjacent ends of the brake shoes, which is acombination of the force of the second shoe return spring and thedistance for said pivotal mount of said brake shoe with said link tosaid shoe return spring, is greater than the moment applied to the firstadjacent ends of the brake shoes, which is a combination of the force ofthe first shoe return spring and the distance from said pivotal mount tosaid shoe return spring.

Claim 7 is a drum brake device as claimed in claim 1, wherein aprotuberance is integrally press-formed on the long link or the centralregion of one brake shoe at said pivot point and is pivotally engaged ina hole respectively bored at said pivot point in said brake shoe or saidlink.

Claim 8 is a drum brake device comprising: a back plate, two brake shoesprovided to face each other on top of said back plate, a service brakeactuator on said back plate between one pair of first adjacent ends ofsaid brake shoes, an anchor block on said back plate between the otherpair of second adjacent ends of the brake shoes, a shoe clearanceadjustment device adjacent to said service brake actuator between saidtwo brake shoes, a parking brake actuator adjacent to said anchor, along link having a middle segment pivotably mounted at a pivot point onthe middle of one brake shoe, one end of said link and the other end ofsaid link respectively functionally engaged to said shoe clearanceadjustment device and said parking brake actuator, wherein a distancefrom the pivot point in the central region of the long link to theparking brake actuator is longer than a distance from said pivot pointto the shoe clearance adjustment device.

Claim 9 is a drum brake device as claimed in claim 8, wherein the longlink operates in tandem with said one brake shoe when the service brakeis applied.

Claim 10 is a drum brake device as claimed in claim 8, in which saidshoe clearance adjustment device senses an amount by which said pair ofbrake shoes has opened and automatically adjusts the clearance betweenthe brake shoes and the brake drum.

Claim 11 is a drum brake device as claimed in claim 8, in which saidstroke adjustment device senses the amount by which said pair of brakeshoes has opened and automatically adjusts the stroke of said parkingbrake actuator.

Claim 12 is a drum brake device as claimed in claim 8, wherein with thepivot point in the central region of said long link as the fulcrum, theresistance to spread open said pair of the brake shoes on said otherside is greater than the resistance to spread open said pair of thebrake shoes on said one side.

Claim 13 is a drum brake device as claimed in claim 12, wherein themoment applied to the second adjacent ends of the brake shoes, which isa combination of the force of the second shoe return spring and thedistance for said pivotal mount of said brake shoe with said link tosaid shoe return spring, is greater than the moment applied to the firstadjacent ends of the brake shoes, which is a combination of the force ofthe first shoe return spring and the distance from said pivotal mount tosaid shoe return spring.

Claim 14 is a drum brake device as claimed in claim 8, wherein aprotuberance is integrally press-formed on the long link or the centralregion of one brake shoe at said pivot point and is pivotally engaged ina hole respectively bored at said pivot point in said brake shoe or saidlink.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and the attendant advantages of the presentinvention will become readily apparent by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings wherein:

FIG. 1 is a plan view of the drum brake device of this invention asembodied in Example 1, Example 3, and Example 5.

FIG. 2 is a cross section view of FIG. 1 taken along line II—II.

FIG. 3 is a cross section view of FIG. 1 taken along line III—III.

FIG. 4 is a cross section view of FIG. 1 taken along line IV—IV.

FIG. 5 is a cross section view of FIG. 1 taken along line V—V.

FIG. 6 illustrates a modified example of FIG. 5.

FIG. 7 is a disassembled view of one brake shore, the long link, andrelated components.

FIG. 8 is a plan view of the drum brake device of this invention asembodied in Example 2.

FIG. 9 is a model diagram that explains the operation of the drum brakedevice of this invention as embodied in Example 2.

FIG. 10 is a partial enlarged plan view of the drum brake device of thisinvention as embodied in Example 3.

FIG. 11 is a cross section view of FIG. 10 taken along line XI—XI.

FIG. 12 is a plan view of the drum brake device of this invention asembodied in Example 4.

FIG. 13 is a partial enlarged plan view of FIG. 1 for the drum brakedevice of this invention as embodied in Example 5.

FIG. 14 is a plan view of the drum brake device of this invention asembodied in Example 6.

FIG. 15 is a cross section view of FIG. 14 taken along line XV—XV.

FIG. 16 is a cross section view of FIG. 14 taken along line XVI—XVI.

FIG. 17 is a plan view of the conventional drum brake device asdisclosed in Australian Patent No. AU-B1-53 491179 on which thisinvention was based.

FIG. 18 is a plan view of the conventional drum brake device asdisclosed in U.S. Pat. No. 5,275,260 on which this invention was based.

FIG. 19 is a model that explains the operation of the conventional drumbrake devices on which this invention was based.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Example 1

Example 1 is generally shown in FIGS. 1-7. FIG. 1 being a plan view ofthe drum brake device. The central hole 1 a of the back plate 1 isfreely inlaid on the vehicle axle and the back plate is affixed to astationary part of the vehicle by four bolts inserted through the boltholes 1 b. A pair of brake shoes 2, 3, are provided to face oppositelyto each other. Each shoe comprises a shoe rim 4, a shoe web 5 joined tothe rim 4 to form a “T” in cross section, and a lining 6 affixed aroundthe perimeter of the shoe rim 4. Friction created as the linings areforced against the brake drum (not shown in the drawing) produces thebraking action. The brake shoes 2, 3 are each mounted on top of the backplate 1 by a shoe-hold mechanism 7, 7, each comprising a known type ofplate spring and pin.

A service brake actuator 8, activated when the service brakes areapplied, is provided between one pair of adjacent ends 2 a, 3 a of thepair of oppositely-facing brake shoes 2, 3, and is affixed to the backplate 1 with bolts or other hardware. A hydraulic wheel cylinder iswidely used as the actuator, but an air wheel cylinder can be used.

An anchor block 9 is provided between the other pair of adjacent ends 2b, 3 b of the two brake shoes 2, 3. The anchor block 9 is normallyaffixed on top of a raised segment of the back plate 1 by two rivets 10,10, but it can be welded if desired. Moreover, an anchor pin can be usedin place of the rectangular plate. In either case, the anchor mustsupport each of the other adjacent ends 2 b, 3 b of the brake shoes 2,3.

A long link 11 is set under the shoe web 5 of one brake shoe 2. Aprotuberance 11 a, formed as burrs with a press is formed in the centerof the link 11, slips into the hole 5 a bored in the shoe web 5. Asshown in FIG. 7, notched grooves 11 c, 11 d are formed in the upper andlower segments, respectively. FIG. 5 illustrates the shape of theprotuberance 11 a; however it can also be formed as drawing with a pressto be an inverse U-shaped protuberance 11 b as shown in FIG. 6. Eitherof the protuberances 11 a or 11 b is integrally formed by a press withthe long link 11, but, a protuberance is integrally formed by a presswith the shoe web 5, slips into the hole bored in the link 11, or aseparate pin can be easily used to support the long link 11 so as to bepivotable on the shoe web.

A shoe clearance adjustment device 12, of a known screw type shown inFIG. 3, adjusts the clearance between the brake drum, and the brakeshoes 2, 3. These Figures illustrate an automatic shoe clearanceadjustment device, to be described later. However, a screw driver can beinserted into the hole 1 c, bored in the back plate 1 or the hole boredin the brake drum (not shown), to turn the toothed adjustment wheel 13 awhich is integrally formed onto the bolt 13. Screwing the toothedadjustment wheel 13 a into or out of the threaded tube segment 14 willmanually adjust the entire length of the shoe clearance adjustmentdevice 12. A socket 15 supports one end of the bolt 13. A thin plate tipis formed on the end of the tube segment 14 and the end of the socket15. The socket 15 and the tube segment 14 engage the brake shoes 2, 3respectively, with a notched groove 14 a, 15 a formed in each plate tiprespectively. The bottom of the notched groove 14 a abuts against thebottom of the notched groove 5 b formed on the shoe web 5 of the otherbrake shoe 3; while the bottom of the notched groove 15 a abuts againstthe bottom of the notched groove 5 b formed with the shoe web 5 of onebrake shoe 2 and the bottom of the notched groove 11 c on the one end ofthe long link 11 as shown in FIG. 3. In reality, however, because of thetolerances in the fabrication of the brake shoe 2, the long link 11, andthe other components, there will be a minimal gap equivalent to thetolerances at the bottom of the notched groove 11 c or 11 d of the longlink 11.

The parking brake actuator 16 is activated when the parking brake isapplied and comprises a forward-pull brake lever 17, a strut 18, andother components. The brake lever 17 is set under the shoe web 5 of theother brake shoe 3. The base end 17 a is pivotable on a pin 19 on theother end 3 b of brake shoe 3. A U-shaped groove, onto which is latchedthe remote control cable (not shown in the drawing) is formed on thefree end 17 b. A stopper 17 c abutting against the inner face of theshoe rim 4 regulates the return position of the brake lever 17 when theparking brake is not activated.

The strut 18 is a clearance adjustment device to adjust the clearancebetween the long link 11 and the brake lever 17. Its structure andfunctions are the same as the shoe clearance adjustment device 12, andits structural components are denoted here with an added apostrophe.These drawings illustrate an automatic stroke adjustment device, to bedescribed later. However, a screw driver can be inserted into the hole1′c, bored in the back plate 1 or brake drum, to turn the toothedadjustment wheel 13′a which is integrally formed onto the bolt 13′.Screwing the toothed adjustment wheel 13′a into or out of the tubesegment 14′ will manually adjust the whole length of the strokeadjustment device.

As shown in FIG. 4, a thin plate tip is formed on the ends of the tubesegment 14′ and socket 15′. Notched grooves 14′a and 15′a, formed ineach plate tip respectively, are engaged with the notched groove 17 d ofthe brake lever 17 and the notched groove 11 d of the long link 11respectively. The strut 18 can be adjusted to have no slack in the axialdirection by the aforementioned manual adjustment.

As shown in FIG. 3, a pipe 20 can serve as the outer casing of theremote control cable (not shown in the drawing). The outer casing of thecable is affixed to the back plate 1. As shown in FIG. 1, an upper orfirst shoe return spring 21, adjacent to actuator 8 activated when theservice brake is applied, is stretched between the one pair of adjacentends 2 a, 3 a of the two brake shoes 2, 3. A lower or second shoe returnspring 22, positioned adjacent to the anchor block 9, is stretchedbetween the other pair of adjacent ends 2 b, 3 b of the two brake shoes2, 3. The mounted loads of the return springs are determined such thatthe ends of the brake shoes 2,3 on the anchor block 9 side do not spreadapart. That is, the first and second shoe return springs 21, 22 areselected so as to satisfy the following relational formula for therespective moment acting on the brake shoes 2, 3:

F1×L1<F2×L2, wherein:

F1: Mounted load of first return spring 21;

F2: Mounted load of second return spring 22;

L1: Distance from the pivot point of brake shoe 2 with link 11 to thefirst return spring 21;

L2: Distance from the pivot point of brake shoe 2 with link 11 to thesecond return spring 22.

When the driver steps on the brake pedal, the service brake actuator 8is pressurized and extends. The one ends 2 a, 3 a of both brake shoes 2,3 spread open, with the point of abutment of the other ends 2 b, 3 bwith the anchor block 9 as the fulcrum. This forces the linings 6, 6against the rotating brake drum, and the friction so created will brakethe vehicle. At this point, either brake shoe 2 or brake shoe 3 has aself-servo function while the other does not, hence the drum brakedevice functions as a leading-trailing type.

The operation of the parking brake is explained next, with eachcomponent turning in the direction as shown in FIG. 1.

For example, when the hand brake lever is pulled, the free end 17 b ofthe brake lever 17 is pulled to the right by the remote control cable(not shown in drawing). At this point, the brake lever 17 turnsclockwise, with the pin 19 on which the free end 17 a pivots as thefulcrum, and presses against the strut 18 with lever-ratio. As the strut18 presses against the notched groove 11 d of the other end of the longlink 11, the link 11 turns counterclockwise, with the protuberance 11 aas the fulcrum. The force of the rotation is transferred to the notchedgroove 5 b of the other brake shoe 3 via the shoe clearance adjustmentdevice 12, wherein the one end 3 a of the brake shoe 3 spreads open,with the other end 3 b as the fulcrum and is pressed against the brakedrum.

Moreover as the brake lever 17 is pulled, a force is generated to turnthe long link 11 counterclockwise, with the one notched groove 11 cabutting the shoe clearance adjustment device 12 as the fulcrum, and theaction force is transferred to the hole 5 a of the one brake shoe 2 bythe protuberance 11 a. At this point, the torque from the mounted loadof the second return spring 22 is large, whereby the brake shoe 2 alsoopens with its other end 2 b as the fulcrum, and is pressed against thebrake drum.

If at this point, a clockwise torque is applied on the brake drum, thenthe friction force of the other brake shoe 3 is transferred to the onebrake shoe 2 via the shoe clearance adjustment device 12, wherein theother end 2 b of the brake shoe 2 is supported by the anchor block 9 togenerate a braking force. Hence the drum brake device functions as aduo-servo type in which both brake shoes 2, 3 have a self-servofunction.

If a counterclockwise torque is applied on the brake drum, then thefriction force of the one brake shoe 2 is transferred to the other brakeshoe 3 via the shoe clearance adjustment device 12, wherein the otherend 3 b of the brake shoe 3 is supported by the anchor block 9 togenerate a braking force. Again the drum brake device functions as aduo-servo type in which both brake shoes 2, 3 have a self-servofunction.

With this configuration, as described previously, the amount ofdisplacement of the notched groove of one brake shoe 2 differs from theamount of the displacement of the notched groove 11 c of the long link11 changes as the linings 6, 6 wear. However, the whole length of thestrut 18 can be adjusted to be extended by a suitable amount, therebyminimizing the stroke of the brake lever 17 and the return stroke of thepiston of the service brake actuator 8. This will preclude a sense ofslackness in the hand brake, as well as any concern about interferencefrom other components.

As is evident from this explanation, the brake shoes 2, 3 do notseparate from the anchor block 9 until the brake drum rotates wheneither the service brake or the parking brake is applied. The effect isobviously the same when both brakes are applied together. Accordingly,the other adjacent end 2 b or 3 b of the brake shoe 2 or 3 respectivelydoes not collide with the anchor block 9 to generate any noise, nor isan impact load applied to the anchor block. That is, the effect differsfrom a conventional device, in which when the parking brake is applied,the brake shoes 2,3 will open completely wherein the other adjacent ends2 b, 3 b will separate from the anchor block 9, thus generating a noisewhen the brake drum starts to rotate and applying an impact load to theanchor block.

In addition, the adjacent ends 2 b, 3 b will not be separated from theanchor block 9 even in the situation that the brake lever 17 is not setits return position precisely, thereby maintaining the stability of thebrake shoes 2, 3 while driving.

Example 2

FIG. 8 illustrates another embodiment of this invention, in which thepivot position of the long link 11 has been changed. Otherwise, allother components are the virtually the same as in Example 1, and areidentified with same symbols wherein an explanation is omitted here.

That is, the link 11 has been designed such that h3>h2, wherein:

h2: Distance from the center of the protuberance 11 a of long link 11 tothe engaging point with the shoe clearance adjustment device 12;

h3: Distance from the center of the protuberance 11 a of long link 11 tothe engaging point with the strut 18.

If the brakes are applied on a slope, in most cases, the vehicle isstopped with the service brake, the parking brake is applied and thepassenger compartment hand lever, not shown in the drawing, is locked,then the service brake is released. During this operation, the one end 3a, 2 a of the brake shoes 3, 2 spread to the left and right, and withits protuberance 11 a as the fulcrum, the long link 11 rotatescounterclockwise, whereby a gap is opened between the bottom of thenotched groove 5 b on the one brake shoe 2 and the bottom of the notchedgroove 15 a of the socket 15 in an amount equivalent to the rotation ofthe long link 11.

If, in this state, a braking force acts to rotate the brake drumclockwise (uphill or downhill), then the other brake shoe 3, brake lever17, and other components rotate in tandem in an amount just to close thegap. In other words, the bottom of the notched groove 15 a of the socket15 will abut against the bottom of the notched groove 5 b of the onebrake shoe 2. However, the lever-ratio of the long link 11 has been setsuch that h3>h2, hence as shown in FIG. 9, the pre-rotation state asindicated by the double-dash broken line shifts to the post-rotationstate as indicated by the solid and broken lines, and the strut 18 isrepelled from the bottom of the notched groove 17 d of the brake lever17 by an amount equivalent to the lever-ratio of the long link 11.

As a result, the free end 17 b of the brake lever 17 is repelled andextends the distance between the free end 17 b and the outlet 20 a by anamount just equal to the distance subtracting the distance I3 afterrotation from the distance I1 before rotation. Therefore there is noincrease in the tension of the remote control device to reduce thebrake's effectiveness, thus precluding any need to get flustered andpump the brake pedal or pull harder on the hand brake lever as withconventional devices.

Moreover the remote control cable, not shown in the drawing, normallywinds underneath the floor of the vehicle, then the other end isconnected to the hand lever inside the passenger compartment. If thefree end 17 b of the brake lever 17 were to shift as explained, the onlychange is that the meander portion of the control cable is slightlystraightened, with no harmful effect on any structural component. It isobvious that the link lever-ratio can be set to any suitable value, asrequired.

Should a counterclockwise braking force act on the brake drum causing itto rotate, neither the other brake shoe 3 nor the brake lever 17 move togenerate any slackness in the remote control cable.

Example 3

Example 3 is another embodiment of this invention shown in FIGS. 1, 3,7, 10, and 11, which is equipped with an incremental type of automaticshoe clearance adjustment device which is activated when the servicebrakes are applied.

A pin 24 affixed on the one end side of the long link 11 freelypenetrates through a slot 5 d bored in the shoe web 5 of one brake shoe2 and a hole 25 a, provided in the middle of the adjustment lever 25.The adjustment lever 25 is pivotable around the stem component 24 a ofthe pin 24 which protrudes above the hole 5 d. One arm 25 b of theadjustment lever 25 abuts against the stepped face 15 b of the notchedgroove 15 a of the socket 15, while the other arm 25 c engages thetoothed adjustment wheel 13 a of the adjustment bolt 13.

Alternatively, the pin 24 can be affixed to the shoe web 5, and theadjustment level 25 can pivot on the stem component 24 a of the pin 24.

An adjustment spring 26 is stretched between another arm 25 d of theadjustment lever 25 and the shoe web 5. As shown in FIG. 10, a partialenlarged plan view of FIG. 1, the adjustment spring 26 biases theadjustment lever 25 so as turn counterclockwise with the pin 24 as thefulcrum. In this state, the perimeter of pin 24 engages with the inneredge of the outer brake side of the slot 5 d. Thus, when the long link11 is temporarily assembled onto the one brake shoe 2, the properalignment of the notched groove 5 b of the one brake shoe 2 and thenotched groove 11 c can be easily ascertained visually.

The automatic shoe clearance adjustment device can be arranged so as tohave left-right symmetry as in FIG. 1. That is, the adjustment lever 25is arranged to be pivotable on the other brake shoe 3 and the shoeclearance adjustment device 12 is arranged with the left and right sidesreversed. A spring mechanism is installed so that the torque thatextends the shoe clearance adjustment device 12 will be applied to theadjustment lever 25. In this case, even if the brake lever 17 were setwith a touch of pulling it, the engaging position of the adjustmentlever 25 and toothed adjustment wheel 13 a does not change, and theautomatic adjustment action will be more stable.

With the configuration of FIG. 1 and FIG. 10, when the service brake isapplied and the two brake shoes 2,3 spread open, the automatic shoeclearance adjustment device 12 trails the other brake shoe 3. On theother hand, the long link 11 trails the one brake shoe 2 in almosttandem at this time. The other arm 25 c of the adjustment lever 25 isturned counterclockwise with the pin 24 as the fulcrum as shown in FIG.10 in an amount equivalent to the sum of the degree of movement of thepin 24 and the amount of movement of the automatic shoe clearanceadjustment device.

At this point, if the linings 6, 6 are worm, and the degree of rotationof the other arm 25 c of the adjustment lever 25 exceeds the intertoothpitch of the toothed adjustment wheel 13 a, the bolt 13 is rotated to bescrewed out of the tube segment 14. This automatically adjusts the gapbetween the brake drum and the linings 6, 6 to maintain a constantclearance.

When the parking brake is applied, the automatic shoe clearanceadjustment device 12, the notched groove 11 c side of the long link 11,the adjustment lever 25 and other components all trail in tandem theother brake shoe 3 just by the amount it opens. However, with the otherbrake shoe 2, the pin 24 is freely inlaid to move within its slot 5 d;hence it has no effect on the adjustment lever 25. As a result, anyautomatic adjustment action will not be less than the movement of theadjustment lever 25 when the service brake is applied.

As is evident from this configuration, the biasing force of theadjustment spring 26 constantly acts on the long link 11, even when theservice brakes are released; hence, the link 11 will not vibrate.

Example 4

The previous embodiment clearly shows that the required functions can beobtained with a configuration in which the long link 11 spreads open intandem with the one brake shoe 2. This example will explain a modifiedversion of that embodiment.

These components which differ from the above-mentioned example aremarked with an apostrophe. That is, whereas, in the above-mentionedexample, the pin 24 fixing on the long link 11 abuts against inner edgeof the outer brake side of the slot 5 d of the one brake shoe 2, thelower face 11′e of the long link 11′ abuts against the anchor block 9.The braking operation and automatic adjustment action of thisconfiguration is the same as for the above-mentioned example, and anexplanation is omitted here.

As shown also in FIG. 12, the same function can be obtained by providingone back edge 11′g of the long link 11′ with the inner face of the shoerim 4′. What is essential is that when the service brake is applied, thelong link 11′ spreads open in tandem with the one brake shoe 2′, andthat when the parking brake is applied, the two components turn relativeto each other.

With this configuration, even as the lining wears, the long link 11′,the adjustment lever 25, and the adjustment spring 26 virtually move intandem with the one brake shoe 2, thus having no effect on the automaticadjustment action to provide a stable adjustment function for a longperiod.

Example 5

An automatic stroke adjustment device which automatically adjusts thestroke of the brake lever 17 is explained, with reference to FIG. 1,FIG. 4, and FIG. 13, (a partially enlarged plan view of FIG. 1). Thosecomponents which have the same function as the previously described shoeclearance adjustment device are marked with an apostrophe.

A pin 27 is mounted on the other side of the shoe web 5 of brake shoe 2,and extends through a hole 25′a bored in the base segment of theadjustment lever 25′. Thus, the adjustment lever 25′ is pivotable aroundthe stem segment of the pin 27. One arm 25′b of the adjustment lever 25′abuts against the stepped face 15′b of the notched hole 15′a of thesocket 15′, while the other arm 25′c engages with the toothed adjustmentwheel 13′a.

Alternatively, the pin 27 can be affixed to the long link 11, and theadjustment lever 25′ can pivot on the stem segment of the pin 27 thatpenetrates freely through the shoe web 5.

An adjustment spring 26′ is stretched between the vertical member 25′dbent in the middle of the adjustment lever 25′ and the hollow portion ofthe protuberance 11 a of the long link 11. The energizing force of thespring acts on the adjustment lever 25′ to turn it clockwise, as shownin FIG. 1, with the pin 27 as the fulcrum.

When the service brake is applied and both brake shoes 2, 3 spread open,the strut 18 constantly presses against the brake lever 17 side, whilethe hole 25′a in base segment of the adjustment lever 25′ and the longlink 11 trail the one brake shoe 2 in tandem. Hence as shown in FIG. 1and FIG. 13, the adjustment lever 25′ will turn clockwise, with the pin27 as the fulcrum, by an amount just equal to the movement.

As the linings 6, 6 wear, if the amount of rotation of the other arm25′c of the adjustment lever 25′ exceeds the intertooth pitch of thetoothed adjustment wheel 13′a, the bolt 13′ is rotated so as to bescrewed out of the tube segment 14′ to maintain the gap with the longlink 11 at a constant value. That is, the stroke of the brake lever 17is maintained at a constant value, thus imparting a better brakeresponse.

Example 6

Example 6 is another embodiment shown in FIGS. 14-16 which is equippedwith a one-shot type of automatic shoe clearance adjustment device foruse when the service brake is applied, and a cross-pull type of parkingbrake. Those components which are the same as in the above-mentionedexample are identified with a 100-series of numbers, for which adetailed explanation is omitted here.

As shown in FIG. 14, these components include a back plate 101, a pairof brake shoes 102, 103 with one pair of adjacent ends 102 a, 103 a andthe other pair of adjacent ends 102 b, 103 b, an actuator 108 activatedwhen the service brake is applied, an anchor block 109, a long link 111with a protuberance 111 a, a notched groove 111 c on one end, a notchedgroove 111 d on the other end and a protuberance 111 f. The protuberance111 f abuts against the outer brake side of the large-diameter hole 105d bored in one brake shoe 102.

That is, the two return springs 21, 22 shown in FIG. 1 are replaced withone return spring 123, a fairly thick wire spring configured in theshape of a slightly obtuse U. The middle segment of the wire spring 123is mounted on top of the anchor block 109, and the two free ends 123 a,123 a are bent so as to latch in the holes 105 c, 105 c bored in the twobrake shoes 102, 103.

The wire spring 123 should be stretched in a location such that when theparking brake is applied, the one ends 2 a, 3 a of the brake shoes 2, 3will open with the anchor block 109 as the fulcrum.

The configuration of the shoe return spring is not limited to that shownhere. A variety of shapes and configurations can be used, such assplitting the second return spring into two segments as configured insome conventional devices.

The automatic shoe clearance adjustment device 112 is configured from aplate adjustment strut 113, a bell crank lever 114, and springs 126,127. The bottom of the notched groove 113 a formed on one end of theadjustment strut 113 abuts against the bottom of the notched groove 111c on one end of the long link 111. Small, short teeth 113 b are carvedin the middle of the strut 113.

The middle segment of the bell crank lever 114 is supported by the stemof a pin 115 so as to pivot on the other end 113 c of the strut 113 andto move lengthwise along the plate face of the strut 113. A fan-shapedarm 114 a on one end of the bell crank lever has small, short teeth 114b carved around its perimeter which mesh with the small, short teeth 113b of the strut 113. The other arm 114 c with a cam face is positionedwith a clearance of δ1 in a rectangular hole 103 c formed in brake shoe103.

An adjustment spring 126 is stretched between the brake shoe 102 and theadjustment strut 113. Another spring 127 is stretched between theadjustment strut 113 and the pin 115. The mounted load of the adjustmentspring 126 is set to be greater than that of spring 127.

A cross-pull type of actuator 116, activated when the parking brake isapplied, is configured from the brake lever 117, the strut 118, andother components. The finger-shaped segment 117 a on one end of thebrake lever 117 abuts against the bottom of the notched groove 103 dformed on the other end of brake shoe 103. The arm 117 b on the otherend of the brake lever 117 penetrates freely through the hole 101 d inthe back plate 101. A mounting hole 117 c for connecting the remotecontrol cable (not shown in the drawing) is bored on the reverseL-shaped end of the arm 117 b. A protuberance 117 d is also formed onthe brake lever 117, and abuts against the reverse side of the backplate 101 to regulate the return position of the lever, but is notrestricted to this configuration.

The components of the strut 118 are marked with an apostrophe. A notchedgroove 114′a formed on one end of the tube 114′ holds the other end ofbrake shoe 103. The middle segment of the brake lever 117 is alsopivotable by the pin 119 at this end. A notched groove 115′a on thesocket 115′ holds the other notched groove 111 d of the long link 111and the one brake shoe 102.

The action of this embodiment when the service brake is applied is thesame as that of the embodiment of Example 1, and when the parking brakeis applied, the only difference is that the brake lever 117 has beenchanged to a cross-pull type. That is, when the mounting hole 117 c ofthe brake lever 117 is pulled by the remote control cable (not shown indrawing) the brake lever 117 pressed against the strut 118 by the pin119 with the point of abutment with the brake shoe 103 as the fulcrum.The force of this action is transferred in sequence to the long link111, automatic shoe clearance adjustment device 112, and finally therectangular hole 103 c of the other brake shoe 103, wherein the one end103 a of brake shoe 103 opens, with the other end 103 b as the fulcrum,and engages the brake drum.

Next, the action force is imparted towards the other side of the brakeonto the protuberance 111 a of the long link 111 with the point ofabutment with the adjustment strut 113 as the fulcrum, wherein the oneend 102 a of brake shoe 102, with the other end 102 b as the fulcrum,also opens and engages with the brake drum.

As is clearly evident, the movements of both brake shoes 102, 103, wheneither the service brake or parking brake is applied, is the same as forthe previous embodiments, and the same effectiveness in operation can beobtained.

When the service brake is applied the two brake shoes 102, 103 spreadopen, the automatic shoe clearance adjustment device 112 receives theaction force of the adjustment spring 126 and trails the one brake shoe102. At this point, if the linings 6,6 are worn, and the amount by whichthe shoes have opened exceeds the total of the clearance δ1 of the bellcrank lever 114 plus the height of the small short teeth 114 b, then thebell crank lever 114 turns such that the automatic shoe clearanceadjustment device 112 is extended by an amount equivalent to one toothonly to close the gap with the brake drum.

When the parking brake is applied, the only action is that theadjustment strut 113 and the bell crank lever 114 move in tandem withthe other brake shoe 103 to the left, and the adjustment spring 126extends to move the one brake shoe 102 to the right as shown in FIG. 14.Thus, there is no effect on the automatic adjustment action.

This invention is not, by any means, limited to the aforementionedembodiments. For example, an incremental type of automatic shoeclearance adjustment device can be combined with a cross-pull type ofparking brake; or a one-shot type of automatic shoe clearance adjustmentdevice can be combined with a forward-pull type of parking brake. Otherexamples include superimposing the long link 11, 11′, 111 on that faceof the shoe web 5 on the side which the brake drum is mounted. A strokeadjustment device can be fitted to the automatic shoe clearanceadjustment device used in the conventional device of U.S. Pat. No.5,275,260 to provide a stable automatic adjustment action for aprolonged period. The possibility of many other variations should beevident to those people technically skilled in this industry.

As is evident from the aforementioned configurations, this inventionprovides the following advantages.

A clearance adjustment device in which, its whole length of a strutsuspended between the brake lever and the long link, can be adjusted,has been set on top of a strut. This ensures a constant stroke of thebrake lever, and no slackness in the hand brake, throughout the life ofthe brake shoe linings.

The relative positions of the one brake shoe and the long link engagingwith the shoe clearance adjustment device are constant along thelengthwise direction of the shoe clearance adjustment device. Hence whenthe parking brake is applied, even if a braking force is applied to thebrake drum causes it to rotate, the piston of the service brake actuatoris returned to a minimal degree. This provides a good service brakeresponse when the service brake is applied after the parking and servicebrake is applied simultaneously.

The lever-ratio of the long link can be changed so that the free end ofthe brake lever is not displaced in the direction to provide a slack tothe remote control cable. Thus there is no reduction in brakingeffectiveness when the vehicle has stopped on a slope and the servicebrake is released after the hand lever has been locked. This frees thedriver from any concerns about rolling upon starting the car in motionagain. The driver need not step on the foot brake again or pull on thehand lever again.

The brake shoes do not separate from the anchor block, even when theparking brake is applied, in which case no noise is generated even whena torque is generated on the brake drum starts, thus eliminating anydiscomfort or anxiety for the driver.

No impact load is applied to the anchor block, hence the strength of itsperiphery can be reduced to make the device lighter.

The end of the brake shoe on the anchor block side can be prevented fromopening solely and easily by a proper setting of the mounting loads ofthe shoe return springs and their positions.

No impact load is applied to any other component as well, which assureslong-term reliability in terms of strength, durability, and otherproperties.

The adjacent ends 2 b, 3 b, will not be separated from the anchor block9 even in the situation that the brake lever 17 is not set in its returnposition precisely, thereby avoiding the unusual dragging between thelining and the drum brake or the wheel being locked when the brake shoebites the brake drum.

It is readily apparent that the above-described has the advantage ofwide commercial utility. It should be understood that the specific formof the invention hereinabove described is intended to be representativeonly, as certain modifications within the scope of these teachings willbe apparent to those skilled in the art.

Accordingly, reference should be made to the following claims indetermining the full scope of the invention.

What we claim is:
 1. A drum brake device comprising: a back plate, twobrake shoes provided to face each other on top of said back plate, aservice brake actuator on said back plate between one pair of firstadjacent ends of said brake shoes, an anchor block on said back platebetween the other pair of second adjacent ends of the brake shoes, ashoe clearance adjustment device adjacent to said service brake actuatorbetween said two brake shoes, a parking brake actuator adjacent to saidanchor, a long link having a middle segment pivotably mounted at a pivotpoint on a middle portion of one brake shoe, one end of said link andthe other end of said link respectively functionally engaged to saidshoe clearance adjustment device and said parking brake actuator,wherein a first distance defined between a horizontal base line,parallel to a horizontal center line, extending centrally through thepivot point located in a central region of the long link and a firsthorizontal line extending along with and through the parking brakeactuator is longer than a second distance defined between the base lineand a second horizontal line extending along with and though the shoeclearance adjustment device.
 2. A drum brake device as claimed in claim1, wherein the long link operates in tandem with said one brake shoewhen the service brake is applied.
 3. A drum brake device as claimed inclaim 1, in which said shoe clearance adjustment device senses an amountby which said pair of brake shoes has opened and automatically adjuststhe clearance between the brake shoes and the brake drum.
 4. A drumbrake device as claimed in claim 1, wherein with the pivot point in thecentral region of said long link as the fulcrum, the resistance tospread open said pair of the brake shoes on said other side is greaterthan the resistance to spread open said pair of the brake shoes on saidone side.
 5. A drum brake device as claimed in claim 4, wherein themoment applied to the second adjacent ends of the brake shoes, which isa combination of the force of the second shoe return spring and thedistance for said pivotal mount of said brake shoe with said link tosaid shoe return spring, is greater than the moment applied to the firstadjacent ends of the brake shoes, which is a combination of the force ofthe first shoe return spring and the distance from said pivotal mount tosaid shoe return spring.
 6. A drum brake device as claimed in claim 4,further comprising a first shoe return spring between one side of saidtwo brake shoes and a second shoe return spring stretched between saidother side of said two brake shoes, wherein with the pivot point in themiddle of said long link as the fulcrum, the torque of the second shoereturn spring is greater than the torque of the first shoe returnspring.
 7. A drum brake device as claimed in claim 1, in which aprotuberance integrally formed by a press onto the middle segment ofsaid long link is pivotable in a hole bored in said brake shoe.
 8. Adrum brake device as claimed in claim 1 in which a protuberanceintegrally formed by a press onto the middle segment of one brake shoeis pivotable in a hole bored in said long link.
 9. A drum brake devicecomprising: a back plate; two brake shoes facing each other on top ofsaid back plate; a service brake actuator mounted on said back plate andpositioned between one pair of adjacent ends of said brake shoes; ananchor block mounted on each back plate and positioned between the otherpair of adjacent ends of the brake shoes; a shoe clearance adjustmentdevice adjacent to said service brake actuator between said two brakeshoes; a parking brake actuator adjacent to said anchor, and a long linkpivotable at a middle segment thereof at a pivot point to a middle ofone brake shoe, said shoe clearance adjustment device and said parkingbrake actuator being functionally engaged on one end and the other endrespectively of said link; wherein a distance from the pivot point inthe middle of the long link to the parking brake actuator is longer thana distance from said pivot point to the shoe clearance adjustmentdevice.